Automotive Electrical/Electronic (E/E)-architectures consist of various components which are generally developed independently. Due to the increasing size and complexity, component integration is highly challenging and already slight modifications to components or subsystems often require expensive re-testing and re-validation. As a remedy, we propose a framework for modular architectures based on a data-centric description and a fully time-triggered scheduling. This modular design approach is enabled by a novel methodology for schedule integration where local schedules are defined independently for subsystems before being integrated into a global schedule. This divide-and-conquer approach significantly reduces the integration complexity while the system becomes highly composable. Our experimental results give evidence of the efficiency and versatility of the proposed approach, using networks based on a time-triggered automotive Ethernet.